The government was defeated on Thursday by just 13 votes in the House of Commons in its bid for a "strong humanitarian response" to the alleged use of chemical weapons by the Syrian regime.

Minutes after the shock result, Cameron told lawmakers: "It is clear to me that the British Parliament, reflecting the views of the British people, does not want to see British military action. I get that, and the government will act accordingly."

Cameron's defeat raises the prospects that the United States could act alone against the government of Syrian President Bashar al-Assad, which it blames for horrific poison gas attacks that are believed to have killed hundreds in the suburbs of Damascus last week.

"Britain will not be involved in any military action," a spokesman for Cameron's Downing Street office confirmed. Seven hours of impassioned debate in the House of Commons had revealed deep divisions over whether military strikes against the Assad regime would deter the further use of chemical weapons, or simply make the conflict worse.

Cameron had made the case for targeted strikes, insisting that Britain could not stand idle in the face of "one of the most abhorrent uses of chemical weapons in a century".

"If nothing is done, (the regime) will conclude that it can use these weapons again and again, and on a larger scale, and with impunity," he had told the Parliament. But he faced strong resistance from the opposition Labour party and many members of his own Conservative party, who expressed fear that Britain was rushing to a war without conclusive evidence that Assad had gassed his own people.

Cameron admitted there could not be "100 percent certainty" about who had committed the attack, but said it was "beyond doubt" that the regime was responsible. Britain's Joint Intelligence Committee released evidence Thursday saying that chemical weapons had undoubtedly been used on August 21 and that more than 300 people had been killed.

It was "highly likely" that the Syrian government was responsible, it added. The regime has denied it committed the attack, which it blames on rebel forces. Britain's Labour party had proposed an alternative motion seeking "compelling" evidence that the regime carried out the attack before committing to any form of military action, but this too was defeated.